This invention pertains to scanning radios, wherein a radio is currently monitoring a first channel of frequency f(1) and desires to check for carrier activity on a second (scanned) channel of frequency f(2).
With present scanning radios using slow-lock synthesizers, the radio waits for a fixed amount of time before checking for carrier activity on the scanned channel. This time is calculated to be sufficient for the worst case of maximum frequency separation between the current channel and the next channel to be scanned. With this arrangement, the radio will leave the active channel frequency f(1) and re-program the synthesizer with the scanned channel frequency f(2). If no carrier activity is detected at frequency f(2), the radio will typically re-program the synthesizer with the prior active channel frequency f(1).
Naturally, this process creates an audible gap in the program on the active channel. For a slow-lock synthesizer, the size of the audible gap is so big that some of the syllables in a verbal communication are missed. Consequently, the conversation being listened to may not be intelligible.
With scanning radios, therefore, it is desirable to minimize the size of the audible gap so that the conversation being monitored is more intelligible.